Books
Reference: do get a copy of (Bantam's) Amiga DOS Reference Manual, the most
recent you can find, but at least covering V2.0 if you can (they may be getting
hard to find). Although users of higher level languages often get a lot of the
DOS stuff inserted as "canned" code, when you work in assembler you'll need to
do more things with DOS. (Things like the RKMs are of course useful, too, for
Amiga programming in ALL languages; but they are hefty and costly, and you
might wish to be selective/gradual in their acquisition).
The DOS Reference Manual appears at first glance to be a guide to CLI/Shell
commands, but in fact it also contains essential technical reference material
in the back half.
"Mapping the Amiga" (Anderson and Thompson, Compute Books) is also a splendid
technical reference/overview that gives you a good deal of information on
libraries and systems structures in compact form.
All this is reference stuff; I'm not sure what to suggest in the way of
currently available tutorial material. Others may know what's around better
than I do. Some of the Fred Fish stuff comes with assembler source, more
commonly with earlier programs.
You should identify your system before asking for certain information. For
example, there are quite a few assemblers available, but some are good only
with DOS 2.0 and subsequent systems.
–Jim